Chapter 13: Stress and workload Describes factors that influence human performance Direct effect on performance (interfere with perception and action) Indirect effect through psychological mechanisms, such as arousal Long-term debilitating effects Objective: To modify the work environment to reduce or eliminate stressors

Objectives Understand range of stressors and their effects (physical and psychological) Workload prediction and measurement Difficulties with monitoring tasks: Vigilance decrement Sleep loss and disruption (circadian desynchronization and sleep quality)

Four effects of stressors Psychological experience Physiological change Information processing performance, usually degrades Long-term health

Environmental stressors Noise Lighting Motion Vibration Whole body vibration Sickness inducing low frequency motion Thermal (heat, cold) Air quality

Psychological stressors Cognitive appraisal Level of arousal Performance decrements with over arousal Perceptual narrowing Cognitive tunneling Working memory loss Revision to dominant behaviors based on LTM Strategic shifts, tendency to take immediate action

Remediation of psychological stressors Change nature of task, more people Simplify design of displays, controls, and procedures Train so emergency procedures are dominant long-term memory Emergency stress management strategies (don’t react immediately)

Workload Workload affects immediate task performance and can degrade future performance through fatigue Considerations for timeline model Distribution of task time should be considered (use 90th percentile) Time required/Time available<.80 to avoid overload TR/TA modulated by resource requirements TR/TA does not equal effort Time stress and task scheduling People focus on tasks believed to be important and available Train to speed processing Train to calibrate importance

Measurement of mental workload Primary task performance Higher workload makes performance worse Secondary task measures Measures of reserve capacity Mental arithmetic, time estimation, memory, reaction time Physiological measures Heart rate variability, pupil dilation Subjective measures

Mental workload measurement dissociations Higher motivation, higher effort, better performance Performance and arousal curve Change in subjective performance criteria Multiple measures are often used to understand particular situation

Underarousal and vigilance Maintaining vigilance in low workload situation can be fatiguing and stressful Effects of vigilance decrement Time Event salience Signal rate Arousal level

Vigilance enhancement: Enhance arousal and make detection easier Signal enhancement Frequent rest breaks Vigilance declines in as little as 20 minutes Introduce false signals Stimulants Caffeine Music Conversation Avoid sleep disruption

Considerations regarding sleep and fatigue Cost and safety consequence of fatigue Affect on performance Factors affecting fatigue Sleep Circadian rhythm Workload and activity Mitigation strategies

Why does alertness matter? Automotive accidents over 24 hours

Why does alertness matter? Error rates in reading meters

Cost of fatigue related accidents 200,000 crashes and 4,000 deaths/year in roadway accidents due to fatigue 70 Billion/year roadway accident costs related to fatigue Fatigue can reduce performance to level of 0.08 BAC after 24 hours of continuous activity

Fatigue and its affect on performance Highly affected Judgment Learning new material Planning Less effected Motor activity/physical tasks Tasks involving highly interesting material

Factors affecting fatigue Time of day (circadian rhythm) Time since last sleep Time on task, hours of work Amount and quality of sleep (sleep debt) Sleep inertia Circadian desynchronization Lack of environmental stimulation

Circadian desynchronization =Circadian rhythm does not match day/night cycle =Mismatch between when your body wants to sleep and when you need to be awake Shift work Fast rotation worse than slow Delayed shift better than accelerated (get up late) An extended day allows the body to extend the circadian cycle in line with the unconstrained 27-hour cycle

Circadian desynchronization Jet lag Eastbound worse than westbound, similar to delayed shift Allow one day for each time zone for recovery Weekend effect

Fatigue mitigation/Endurance management Get more and better sleep: Sleep hygiene/management No caffeine before bed Consistent sleep periods, with 8 hours per day in a single period Attitude, as in medical interns Quiet, dark place to sleep Napping More than 15 minutes, but no more than 90 minutes Stop at least 10 minutes before work

Fatigue mitigation/Endurance management Sleep credit: sleep more before sleep deprivation period Less effective: Drugs Melatonin, to support circadian synchonization Caffeine, to boost alertness Less practical: Curtail operations Siesta Avoid nighttime operations

Objectives Understand range of stressors and their effects (physical and psychological) Workload prediction and measurement Difficulties with monitoring tasks: Vigilance decrement Sleep loss and disruption (circadian desynchronization and sleep quality)